Cathode active material for lithium secondary battery and lithium secondary battery including the same

A cathode active material for a lithium secondary battery according to an embodiment of the present invention includes a lithium-transition metal oxide particle. The lithium-transition metal oxide particle has a FWHM ratio measured by an in-situ X-ray Diffraction spectroscopy (XRD) and defined by Equation 1 of 400% or less. Life-span properties of a lithium secondary battery can be improved by preventing deformation of a lattice structure and/or a crystal structure in the lithium-transition metal composite oxide particles.